I bought a D600 earlier this year, jumping up from a D5100, and absolutely love it so far. For your purposes, I guess it depends on what you want to shoot. The reason I went full-frame instead of with the D7100 is because I mostly like to shoot landscapes, so the extra dynamic range and greater true wide-angle lens options sealed the deal for me. The new 18-35G lens alongside a 70-xxx is a great combo. Add a 50 1.8 in the middle and you can do a lot of fun shooting. The D7100 looks also to be a great camera if you want to keep your DX glass.